Over the past few years, we have perfected a technique that allows rapid, reproducible determinations of the rheological properties of blood over a wide range of shear rates, using either fresh or anticoagulated samples. We have found significant variations in such properties within a number of research populations. The objective of the present investigation is to apply this technique to study a group of variables known to influence blood rheology, such as anticoagulants, shear rates, age and sex; and to evaluate rheological parameters as predictors of acute vascular accidents (e.g. coronary risk).